Wiring device



G. B. BE NDER WIRING DEVICE April Filed Feb. 24, 19s? lll Inventor George B n His AttOp eg Patented Apr. 2, 1940 UNITED STATES PATENT OFFICE WIRING DEVICE George B. Benander, Yalesville, Conn., assignor to Monowatt Electric Corporation, Bridgeport, Conn., a corporation of Connecticut Application February 24, 1937, Serial No. 127,448

3 Claims. (Cl. 173-322) The present invention relates to wiring devices and particularly to strain reliefs for the conductors connected thereto.

An object of my invention is to provide an improved strain relief which is simple in structure, which can be applied readily to a wiring device at low cost, and which is unusually eflicient in use, being capable of withstanding a strong pull on the conductors without damage to the connection.

Another object of my invention is to provide an improved method of applying a strain relief to a wiring device which method is easily carried out.

My invention is applicable to various wiring devices. It is well adapted for use with heater plugs and it is this application which I have elected to illustrate and describe herein. It is to be understood, however, that the invention is not limited thereto.

In the drawing, Fig. 1 is a side view of a heater plug to which my invention may be applied and illustrating one step in carrying out my method; Fig. 2 is a face view of the inside of a heater plug embodying my invention; and Fig. 3 is a sectional view of the heater plug.

Referring to the drawing, I indicates the casing of a heater plug comprising two complementary halves fastened together by bolts 2. Inside the casing are two chambers 3 and 4 in which are located the two connectors 5, each provided with binding screws 6 for connecting the conductor wires 1 to the connectors. The conductor wires enter through an opening 8 at one end of the casing and extend through passages 8 to the binding screws 6. The other end of the casing is provided with passages 9 which communicate with chambers 3 and 4 and through which contacts enter to engage the connectors. Surrounding opening 8 is an annular groove ill in which is located the enlarged inner end of a coiled wire tube ll through which conductor wires 1 pass and which serves as a guard for the wires. At its outer end, tube H is provided with a handle l2 which may be used in disconnecting the plug from a heating device.

The heater plug so far described is a known construction and is to be taken as typical of any suitable heater plug structure. The casing in such plugs is formed usually from a suitable molding compound such as an artificial resin provided with a filler, for example, a phenolic condensation product having a wood fibre filler. Such molding compounds and their use are well understood. When molded and cured, there is provided a hard, infusible insulating material.

According to my invention, I provide in the casing in the vicinity of the point where the two wires divide to go to the respective connectors a passage II which may extend through only one half of the casing or entirely through the casing. Preferably I extend the passage through both halves of the casing. In any event, the passage l4 communicates with the opening 8 and the passages 8 for wires 1. Then after the device has been wired and the two halves of the casing fastened together in the usual manner, I insert uncured rubber through passage l4, forcing it in around the conductors and filling for a distance the opening 8 and passages 8 after which the rubber is cured by heating. The forcing of the rubber through opening 8, may be done in a suitable heater press so that the inserting of the rubber and its curing becomes a single operation. In Figs. 2 and 3, the cured rubber is indicated at l5.

In connecting conductor cord to a heater plug, the outer insulation l6, that is, the insulation around both wires, is removed to expose the two separately insulated wires for some distance and the insulation I! on the individual wires is removed to bare the ends of the conductors for connection to the binding posts. Usually the insulation l6 terminates at about the inner end of opening 8, the two insulated wires there separating and extending through passages 8 one to each binding post. As will be seen from Figs. 2 and 3, the rubber embeds the end of insulation l6 and the portions of the wires adjacent thereto with insulation l1 thereon and when cured is firmly attached thereto. The passages it are filled with the rubber I5 and there is considerable adhesion between the rubber and the casing. Thus, the wire is firmly anchored in the plug casing by the rubber insert l5. As a result any pull on the wire will be taken by the rubber l5 and will not be transmitted to the binding post connections.

In the present instance, the inner end of the wire tube II and annular groove l0 are illustrated as being embedded in the rubber and in a heater plug of this particular construction, this also serves to anchor the rubber in the casing. The fact that the opening 8, passages 8 and opening it are at an angle to each other, as shown by Figs. 1 and 2, assists also in anchoring the rubber in the casing.

My invention may be used with heater plugs of various constructions and with other types of wiring devices, and various arrangements may be used for insuring that the rubber is firmly anchored in the casing or base of the wiring device. Ordinarily, the rubber in the opening through which it is introduced into the casing and the adhesion between the rubber and the casing is sufiicient to anchor the rubber in position in the casing. I

In the case of heater wire, insulation I! may comprise in part a covering of asbestos fibres which is laid on rather loosely and which frays when insulation I6 is removed. When rubber I5 is embedded around the wires, the insulation l1 becomes embedded therein so that any frayed insulation is covered by the rubber and firmly held. This is a matter of considerable importance in connection with the wiring of heating plugs as the fraying of the insulation is sometimes troublesome.

I have found in connection with heater plugs embodying my invention that the cord will readily withstand a pull of fifty pounds or more without injury to the connections. This pull is greater than that required ordinarily to remove the plug from the device to which it is connected so that even though the user of the plug removes it from the device to which it is connected by jerking the cord, no harm to the heater plug connection results.

While I have referred specifically to uncured rubber as the substance used in carrying out my invention, it is to be understood that my invention is not limited necessarily to the use of rubher but that I may use any other suitable substance or material which can be injected or forced into the casing of a wiring device after the same has been wired and which will harden or set or may be cured to provide a means which grips a portion of the wire and anchors it to the casing.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a wiring device, the combination of a casing of insulating material having contacts therein, an opening for a conductor cord and passages leading from said opening to said contacts, a cord guard having its inner end located in said opening, a conductor cord extending nection between the cord and contacts compris ing material forced into said casing and molded around the cord and the inner end of the cord guard within said opening and passages.

, 2. In a. device of the class described, a casing of insulating material having contacts therein, an opening for a conductor cord and passages leading from said opening to said contacts, a second opening communicating with said passages at an angle thereto, a cord guard having one end located in said first-named opening, a conductor cord extending through said first-named opening and said passages and connected to said contacts, and a strain relief comprising material forced through said second opening and molded around a portion of said cord and the end of said cord guard and extending into said first-mentioned opening, said passages and said second opening.

3. In a device of the class described, a casing of insulating material having contacts therein, said casing having an opening for an electrical conductor, passages extending substantially at right angles to said opening and leading from said opening to said contacts and a second opening extending at another angle to said first-mentioned opening and communicating therewith and with said passages, a cord guard comprising a tubular spring having one end located in said first-mentioned opening, an electric cord having conductors extending through said tubular spring, said first-named opening and said pas-- sages and connected to said contacts, and a strain relief for the connection between said conductors and contacts comprising material forced through said second opening and molded around a portion of said cord and conductors and the end of said spring and extending into said first-mentioned opening, said angularly disposed passages and said second opening to secure the electric cord to said casing.

GEORGE B. BENANDER. 

